Signalling channel and radio system for power saving in wireless devices

ABSTRACT

Wireless devices, transmitters, systems and methods are provided that have a narrow band signalling channel and a wide band channel, for example an OFDM channel. In order to save power, the wireless device is nominally powered down with the exception of a receiver specific to the narrow band signalling channel. Once instructed to do so over the narrow band signalling channel, the wireless device wakes up the rest of its wide band receive circuitry.

This application is a continuation of U.S. patent application Ser. No.10/948,124 and claims the benefit thereof.

FIELD OF THE INVENTION

The invention relates to systems and methods for communicating withwireless terminals in a manner that is efficient in terms of powerconsumption.

BACKGROUND OF THE INVENTION

Power supply management is a significant challenge in terminal and smartsensor design. This is because such terminals and sensors typically havea limited battery capacity. Anything that can be done to reduce powerconsumption for such wireless terminals and sensors would be of benefit.

Traditional terminal/receiver designs drain a large amount of power evenif the terminal is in an idle or dormant mode. The reason for this isthat the terminals are required to monitor a paging channel or a beaconchannel all the time.

OFDM (orthogonal frequency division multiplexing) terminals typicallydrain even more power than CDMA/TDMA (code division multiple access/timedivision multiple access) terminals due to the fact that such terminalsrun their wide band and high resolution ADC (analog-to-digitalconverter) and FFT (Fast Fourier Transform)/sub-FFT engines all thetime, or at least during any period that detection of any signals is tobe possible.

For example, an OFDM terminal in sleep mode will typically periodicallywake up to see if it has any messages. However, conventional terminalsmust perform processing on the full OFDM bandwidth to see if there areany messages. This takes a significant amount of power because a fullanalog-to-digital conversion on the entire bandwidth of the OFDM systemmust be performed together with the processing of the whole digitizeddata block in terms of data buffering, framing, full FFT computationetc. Typically, the paging channel is transmitted at a particular timeand frequency with the same processing engine as the main task channelsand the terminal must wake up in order to look at the paging channel.

It is also noted that due to the high peak-to-average power ratio, theADC needs to cover a high dynamic range, and this also increases thepower consumption.

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides a wireless devicecomprising: a wide band receiver adapted to receive a wide band signal;and a narrow band receiver adapted to receive a narrow band signal, andto process the narrow band signal to determine whether or not to wake upthe wide band receiver, and to wake up the wide band receiver if sodetermined.

In some embodiments, the narrow band receiver is a passive device.

In some embodiments, the narrow band receiver is a semi-passive device.

In some embodiments, the wide band receiver is an OFDM receiver.

In some embodiments, the wide band signal comprises an OFDM signal withzeros inserted at sub-carrier location(s) where the narrow band signalis to reside.

In some embodiments, the wireless device comprises a power supply and aswitch connecting the power supply to the wide band receiver undercontrol of the narrow band receiver, wherein waking up the wide bandreceiver comprises controlling the switch to supply power to the wideband receiver.

In some embodiments, processing the narrow band signal to determinewhether or not to wake up the wide band receiver comprises demodulatingand decoding the narrow band signal and checking if the narrow bandsignal has a message for this wireless device or not.

In some embodiments, the wide band receiver is a CDMA receiver and thewide band signal is a CDMA signal.

In some embodiments, the signalling channel occupies a spectrum adjacentto a spectrum of the CDMA signal.

In some embodiments, the narrow band receiver wakes itself up on aperiodic basis.

According to another broad aspect, the invention provides a transmitteradapted to generate a signal containing a wide band signal and a narrowband signal, wherein the narrow band signal contains informationinstructing particular wireless devices to wake up to receive the wideband signal.

In some embodiments, the transmitter comprises: a first IFFT functionhaving a plurality of data inputs, and at least one zero input in afrequency location(s) where the narrow band signal is to reside; asecond IFFT having zero inputs at frequency locations corresponding tothe plurality of data inputs, and at least one signalling channel inputin the frequency location(s) where the narrow band signal is to reside.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs, and at least one zero input in a frequencylocation(s) where the narrow band signal is to reside; a narrow bandmodulator for generating the narrow band signal operating at asignalling channel frequency where the zeros were inserted.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs; a narrow band modulator for generating thenarrow band signal operating at a signalling channel frequency out of anoperating bandwidth of the wide band signal.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs, and at least one zero input in a frequencylocation(s) where the narrow band signal is to reside; a narrow bandmodulator for generating the narrow band signal operating at multiplefrequencies.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs, and at least signalling channel input in afrequency location(s) where the narrow band signal is to reside.

In some embodiments, the transmitter comprises: a main CDMA signalgenerator operating in a CDMA bandwidth for generating a main CDMAsignal; a signal channel generator operating at an edge of the CDMAbandwidth for generating the narrow band signalling channel.

In some embodiments, the transmitter comprises: a main CDMA signalgenerator operating in a CDMA bandwidth for generating a main CDMAsignal; a signal channel generator operating outside the CDMA bandwidthfor generating the narrow band signalling channel.

According to another broad aspect, the invention provides a methodcomprising: communicating a wide band signal; and communicating a narrowband signal, the narrow band signal indicating whether or not to wake upa wide band receiver.

In some embodiments, the communicating the wide band signal and thenarrow band signal comprise transmitting these signals.

In some embodiments, the communicating the wide band signal and thenarrow band signal comprises receiving these signals.

In some embodiments, the wide band signal is OFDM signal with zerosinserted at sub-carrier location(s) where the narrow band signal is toreside.

In some embodiments, the method further comprises: examining the narrowband signal to determine whether or not to wake up the wide bandreceiver; waking up the wide band receiver if so determined.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the attached drawings in which:

FIG. 1 is a frequency plan of an example implementation of a downlinksignalling channel provided by an embodiment of the invention;

FIG. 2A is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signalling channel according to anembodiment of the invention;

FIG. 2B is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signalling channel according to anembodiment of the invention;

FIG. 2C is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signalling channel according to anembodiment of the invention;

FIG. 2D is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signalling channel which hascenter frequency at a certain frequency that may not necessarily belocated inside the OFDM spectrum according to an embodiment of theinvention;

FIG. 3 is a block diagram of a wireless device adapted to receive anarrow band signalling channel in accordance with an embodiment of theinvention;

FIG. 4 is a block diagram of another wireless device adapted to receivea narrow band signalling channel in accordance with an embodiment of theinvention;

FIG. 5 is a block diagram of a CDMA transmitter that is adapted togenerate a narrow band signalling channel in accordance with anembodiment of the invention; and

FIG. 6 is an example of spectrum utilization for a UMTS wireless deviceadapted to receive a narrow band signalling channel in accordance withan embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to reduce the power consumption of a wireless device due to theprocessing of the received paging channel or similar channels, a newsignalling channel is provided for use in OFDM systems. The bandwidth ofone or more tones or pieces of spectrum are pre-assigned at a certainfrequency or frequencies. One of the tones or one piece of spectrum ortheir combinations is used for signalling. The new signalling channelmight contain beacon channel information or paging channel informationor system information to name a few examples. The total bandwidth ofthis particular channel can be selected depending upon the designatednetwork capacity. In some embodiments, this channel information ismodulated in the time domain, for example as a PSK (phase shift keying)signal or as an AM signal or otherwise. In another embodiment, thechannel information is modulated in the frequency domain similar toOFDM. In some embodiments, the signalling channel is encoded andmodulated separately from the remaining of the OFDM transmission andtherefore the paging channel can be implemented as a separate module tohook up to a primary radio responsible for the generation of the fullOFDM signal, and preferably with constant modulation. The OFDMsub-carriers are zeroed out if the signalling channel is designed withinband. In other embodiments, the signalling channel can be implementedtogether with the OFDM transmitter. The portion of the transmitterresponsible for generation of the full transmit signal will be referredto as the primary transmitter.

Referring now to FIG. 1, shown is an example of the downlink signallingchannel. Generally indicated at 10 is the typical occupied OFDMspectrum. It can be seen that this consists of a contiguous set ofsub-carriers. The number of sub-carriers will vary for differentapplications. According to an embodiment of the invention, a portion ofthe spectrum is reserved, referred to as the reserved spectrum 12. Thereserved subcarriers can be anywhere inside the spectrum 10. Within thisspectrum, there is transmitted a signal which occupies an occupiedsignalling channel spectrum as indicated at 14. The occupied signallingchannel spectrum is designed so as to fall completely within thereserved spectrum 12.

Preferably, the signalling channel bandwidth is an integer multiple ofthe sub-carrier bandwidth.

Referring now to FIG. 2A, shown is a block diagram of a first example ofan OFDM transmitter capable of generating a narrow band signallingchannel in accordance with an embodiment of the invention. Thesignalling channel in this example is implemented in the frequencydomain by the primary transmitter. Shown is an IFFT function 60 havingeight inputs consisting of six data inputs 62 and two signalling channelinputs 64. The IFFT produces a time domain output which is input to aparallel-to-serial converter 66 to produce an overall output 68. In thiscase, a single IFFT 60 is employed to produce the overall outputcontaining both the wide band content and the signalling channelcontent. In this example and the examples that follow, it is to beunderstood that the number of sub-carriers and the particular locationof the sub-carriers for data and signalling are particular to theseexamples, but that more generally any number of sub-carriers can beemployed for a wide band content, and the narrow band signalling channelcan be inserted anywhere within the wide band spectrum. Preferablyhowever, the signalling channel is inserted at the edge of the availablespectrum, and occupies as few sub-carriers as possible to control thesystem overhead.

Referring to FIG. 2B, shown is another example of a transmitter adaptedto produce a signal containing both the wide band output and thesignalling channel. In this case, the signalling channel is implementedin the frequency domain separately from the primary transmitter. Shownis a first IFFT function 70 receiving as input data inputs 72, and zeroinputs 74 in the frequency locations where the signalling channel is toreside. The output of IFFT 70 is converted to serial form withparallel-to-serial converter 76 to produce a wide band time domainoutput 78. Similarly, a second IFFT function 80 is shown having zeroinputs 82 where the wide band data content is to be located, and havingsignalling channel inputs 84 at the frequency locations where thesignalling channel is to reside. The IFFT 80 produces a time domainoutput which is converted to serial form with parallel-to-serialconverter 86 to produce a signalling channel time domain output 88. Thetwo time domain outputs 78,88 are combined at 90 to produce an overalloutput 92.

A third example of a transmitter for generating an overall outputcontaining the OFDM signal and narrow band signalling channel is shownin FIG. 2C. In this example, the signalling channel is separatelydesigned within the reserved spectrum and may or may not involve IFFTfunctionality. In this case the OFDM functionality for the wide bandsignal is the same as that of FIG. 2B, and a wide band time domainoutput is produced at 78. Also shown is a narrow band modulator 96operating at signalling channel frequency. This takes signalling channelinformation 94, modulates it at the signalling channel frequency toproduce the signalling channel output 98 which is combined at 100 withthe wide band time domain output 78 to produce an overall output 102.

A fourth example of a transmitter for generating an overall outputcontaining the OFDM signal and narrow band signalling channel is shownin FIG. 2D. In this case, the OFDM functionality for the wide bandsignal is the same as that of FIG. 2B, and a wide band time domainoutput is produced from data inputs 95 at 78. Also shown is a narrowband modulator 99 operating at a certain signalling channel frequency.This takes signalling channel information 97, modulates it at thesignalling channel frequency to produce the signalling channel output 93which is separately transmitted and of course time synchronized with theprimary transmitter. Depending on the frequency location of the narrowband channel, it may or may not be necessary to insert zeros for one ormore sub-carriers of the OFDM signal. This signalling channel may or maynot share hardware such as RF front end, antenna, etc. with the rest ofthe transmitter.

Four very specific examples of OFDM modulation have been shown in FIGS.2A, 2B, 2C and 2D. Of course a transmitter would typically include farmore functions than those shown in these figures. The minimum detailsnecessary to illustrate how the signalling channel can be modulated havebeen included. Also, it is to be understood that the IFFT is but oneexample of a function for generating an OFDM signal.

Referring now to FIG. 3, shown is a block diagram of a wireless deviceprovided by an embodiment of the invention. The terminal features a wideband receiver 16 and a narrow band receiver 18. Also shown is antennafunctionality generally indicated by 20. The antenna functionality mayconsist of a single or multiple antennas connected to both of thereceiver 16 and 18, or may consist of respective antennas connected toeach of the receivers 16 and 18. The narrow band receiver 18 operates toreceive a narrow band signalling channel, and to decide on the basis ofthe narrow band signalling channel whether or not to generate a wake upsignal 22 to wake up the wide band receiver 16. This wake up signal cancome in any appropriate form. For example it might simply be a signal toswitch on a power supply driving the wide band receiver 16. The signalmay contain scheduling information. Once the wide band receiver is on,it will stay on until it is deemed acceptable to power down again. Thismay occur for example after the completion of a transmission of a datapackage after which the wireless device will power down and wait foranother wake-up.

Referring now to FIG. 4, shown is a block diagram of an example wirelessdevice adapted to process both the regular OFDM channel and thesignalling channel, as provided by an embodiment of the invention. Shownare only some of the key conventional components of an OFDM receiver forillustration purposes, these consisting of a receive antenna 20, receiveduplexer filter 22, RF receiver 24, analog base-band processor 26. Thereis a power management module 36 connected to both the RF receiver 24 andthe analog base-band processor 26. The analog base-band processor 26 andthe power management module 36 are also both connected to a DSP (digitalsignal processor) microprocessor 28. The DSP microprocessor 28 isconnected to memory 30 which might be flash memory, ROM or SRAM to namea few examples. It is also connected to a display 32 and keypad 34.Finally, there is shown a SIM card 42 having an IP address. Thecomponents described thus far all form part of an example of aconventional OFDM receiver. More generally, any set of functionalitythat is capable of performing normal reception of OFDM signals iscontemplated in place of the above described functionality.

In addition to the conventional receiver, there is a narrow bandreceiver 38 also shown connected to the antenna 20 via filter 22. Thenarrow band receiver is connected to a module where a subscriberidentifier, network information, etc. are stored, for example a SIMcard.

Also shown is a battery 40. Battery 40 is connectable to the powermanagement module or not 36 by power switch 37 depending on instructionsfrom the narrow band receiver 38.

The arrow 39 from narrow band receiver 38 to power switch 37 representsan instruction arrow rather than wiring connection. The dotted arrowfrom battery 40 to narrowband receiver 38 is an optional real connectionfrom which the narrowband receiver may drain power for housekeepingpurposes and internal clock purposes etc. The narrow band receiver mayalternatively have its own battery for housekeeping that is separatefrom the main battery. The narrow band receiver 38 is designed to onlylook at the signalling channel. This can be done in a much more powerefficient manner than would be the case in receiving a paging channelusing all of the conventional receiver circuitry.

In some embodiments, the narrow band receiver 38 is on constantly and iscapable of receiving a message at any time. In another embodiment, thenarrow band receiver 38 wakes itself up on a periodic/scheduled basis.This may for example be achieved by running an internal clock parasiteon the primary radio clock such that after system sychronization, thenarrow band receiver knows when and where the paging channel appears.This latter approach is more power efficient. Once the narrow bandreceiver 38 receives a message for the particular terminal, it will thenwake up the remainder of the wireless device by switching power switch37 over to the power management module 36 such that the terminal is thenoperating in a conventional manner over the entire OFDM spectrum.

In some embodiments, the narrow band receiver 38 does not operate whenthe remainder of the wireless devices are operating in wide bandreceiving mode. In another embodiment, the narrow band receiver 38continues to receive power and to operate even while the remainder ofthe wireless device is powered on.

Not shown in FIG. 4 is all of the circuitry involved for wide-bandtransmission. In duplex implementations, such circuitry would beincluded. However, for the signalling channel, there is only receivefunctionality.

In some embodiments, this new narrow band channel is a replacement foran existing paging channel within the wide-band spectrum. Alternatively,the new signalling channel is used as described, but the existingchannel can also be used to communicate to terminals that are fullypowered. In some embodiments, the narrow band receiver is completelypassive, and does not require any power supply whatsoever. Examples ofreceivers that would be capable of functioning in this manner are MEMSresonators, MEMS RF receivers, or circuits that are capable ofcollecting RF energy from transmitters via inductive coupling circuitry.All the receiver needs to be able to do is to receive and process enoughof the signal to identify if there is a message for the particularwireless device.

In other embodiments, the narrow band receiver is semi-passive, having asmall power supply for house keeping purposes or obtaining a smallamount of power from the main power supply. In such an embodiment, poweris supplied from the battery for house keeping purposes. However, thereis still passive circuitry for collecting RF energy that is then used toprocess the paging channel and to turn on/off the power for the mainradio. FIG. 4 shows a passive power source 33 that might be used inpassive or semi-passive implementations.

Referring now to FIG. 5, shown is a block diagram of another transmitterin accordance with an embodiment of the invention. This embodiment isparticular to CDMA signals. Shown is a main CDMA signal generator 110that generates a wide band CDMA signal 114. Also shown is a signallingchannel generator operating at the edge of the CDMA bandwidth 112 thatproduces a signalling channel output 116. This is combined with the wideband signal 114 at 118, and the sum 119 is up converted at 120 toproduce an overall output 122. The corresponding receiver is similar tothat of FIG. 3 or 4, but with the wide band receiver being a CDMAreceiver.

FIG. 6 shows an example of spectrum utilization for the embodiment ofFIG. 5 specific to a 3GPP/UMTS wireless device. Such wireless devicesemploy signals occupying a 5 MHz bandwidth. The original chip rate forthis standard was 4.096 MCPS (mega chips per second). However, due to achange in the standard now the chip rate is 3.84 MCPS. This results inan amount of extra bandwidth equal to 4.096−3.84=256 kHz. This is enoughfor two narrow band channels with a 128 kHz bandwidth each. This isshown in FIG. 6 where the UMTS signal bandwidth is generally indicatedat 50, and the leftover bandwidth at 52 is now used for narrow bandsignalling channels as described above.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A transmitter configured to generate a signal containing a wide bandsignal and a narrow band signal, wherein the narrow band signal containsinformation instructing particular wireless devices to wake up toreceive the wide band signal, the transmitter comprising: an IFFTfunction having a plurality of data inputs for generating the wide bandsignal; a narrow band modulator for generating the narrow band signaloperating at a signalling channel frequency out of an operatingbandwidth of the wide band signal.
 2. A transmitter configured togenerate a signal containing a wide band signal and a narrow bandsignal, wherein the narrow band signal contains information instructingparticular wireless devices to wake up to receive the wide band signal,the transmitter comprising: an IFFT function having a plurality of datainputs for generating the wide band signal, and at least one zero inputin a frequency location(s) where the narrow band signal is to reside; anarrow band modulator for generating the narrow band signal operating atmultiple frequencies.
 3. The transmitter of claim 2 wherein: the narrowband modulator outputs at least signalling channel output in a frequencylocation(s) where the narrow band signal is to reside.
 4. A transmitterconfigured to generate a signal containing a wide band signal and anarrow band signal, wherein the narrow band signal contains informationinstructing particular wireless devices to wake up to receive the wideband signal, the transmitter comprising: a main CDMA signal generatoroperating in a CDMA bandwidth for generating a main CDMA signal that isthe wideband signal; a signal channel generator operating at one of: anedge of the CDMA bandwidth for generating a narrow band signallingchannel that includes the narrow band signal: or outside the CDMAbandwidth for generating a narrow band signalling channel that includesthe narrow band signal.
 5. A method comprising: communicating a wideband signal; and communicating a narrow band signal, the narrow bandsignal indicating whether or not to wake up a wide band receiver.
 6. Themethod of claim 5 wherein the communicating the wide band signal and thenarrow band signal comprise transmitting these signals.
 7. The method ofclaim 5 wherein the communicating the wide band signal and the narrowband signal comprises receiving these signals.
 8. The method of claim 5wherein the wide band signal is OFDM signal with zeros inserted atsub-carrier location(s) where the narrow band signal is to reside. 9.The method of claim 7 further comprising: examining the narrow bandsignal to determine whether or not to wake up the wide band receiver;and waking up the wide band receiver if so determined.